Voltage reading @idle
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Elder User
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Voltage reading @idle
What should a proper voltage reading be at idle? My current reading is just under 13 volts. Should it not read at least 14 volts or higher? if so, what would be the culprits...battery? alternator? voltage regulator? and how can I isolate the problem and correct it? Thank you.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
13.8 to 14.3 somewhere in there at idle, measure at the battery posts. Spool rpm up to a fast idle and turn on headlights and heater fan, radio etc to put a load on the alternator and measure. It will sag a little maybe. Here's a really good website for troubleshooting, let us know what you find:
http://www.aa1car.com/electrical.htm
Test battery as well, a defective battery may have damaged the alternator to begin with, you don't want to ruin its replacement.
http://www.aa1car.com/electrical.htm
Test battery as well, a defective battery may have damaged the alternator to begin with, you don't want to ruin its replacement.
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Elder User
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That link was very helpful, thanks again! The battery is fully charged (12.8v w/engine not running) 14.2v w/engine running, both measurements taken at the battery posts, so I can safely assume both alternator and regulator are functioning correctly?
Perhaps the gauge itself is defective? it's reading approx. 1.3v less than the readings I get at the battery posts.
Perhaps the gauge itself is defective? it's reading approx. 1.3v less than the readings I get at the battery posts.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
For accuracy, directly at the battery posts is best. Where or how are you measuring that you get a different number? It sounds like everything is good. Make sure belt is properly tensioned, and cable ends are clean and tight at both ends.
Yeah, it's a pretty comprehensive website init?
Yeah, it's a pretty comprehensive website init?
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Elder User
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It's an aftermarket (AutoMeter) volt meter gauge that's mounted in the dash, somewhere between the battery and the gauge it's reading approx. 1.3v less than the battery posts reading. I will take your suggestion and check/clean all my cable connections and grounds.
Lead Driver
Joined: Jul 2017
Posts: 9,609
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From: San Jose, CA
Check specifically the ones that the dash gauge is connected to. Otherwise you may never find out what's up.
If the hand-held meter shows the expected higher voltage, then the gauge itself (or the wiring between the splice and the gauge) is at fault.
If the point of reference for the gauge wiring is actually showing the same loss in voltage with your meter, then your truck's wiring is at fault.
It's not uncommon (even thirty years ago) for some of the wiring to show voltage losses. In a perfect world there would not be any loss throughout the system. But the longer the wire, the smaller the wire gauge (and those two go hand-in-hand), the more likely a measurable loss.
Then you add old age, deteriorating splices and connections and components, and you will really start to see losses. The Ford factory wiring splices (main ones inside the harness tape) are extremely well done and reliable. But even those can deteriorate over time. And of course there are the dreaded PO modifications. Or worse still, PO "fixes" added to the list!!!!! Oy!
Generally if you see less than half of a volt loss in any location, it's not enough to give yourself headaches over. But a lost anywhere of more than a volt is reason for diving in and checking things out.
Good luck.
Paul
If the hand-held meter shows the expected higher voltage, then the gauge itself (or the wiring between the splice and the gauge) is at fault.
If the point of reference for the gauge wiring is actually showing the same loss in voltage with your meter, then your truck's wiring is at fault.
It's not uncommon (even thirty years ago) for some of the wiring to show voltage losses. In a perfect world there would not be any loss throughout the system. But the longer the wire, the smaller the wire gauge (and those two go hand-in-hand), the more likely a measurable loss.
Then you add old age, deteriorating splices and connections and components, and you will really start to see losses. The Ford factory wiring splices (main ones inside the harness tape) are extremely well done and reliable. But even those can deteriorate over time. And of course there are the dreaded PO modifications. Or worse still, PO "fixes" added to the list!!!!! Oy!
Generally if you see less than half of a volt loss in any location, it's not enough to give yourself headaches over. But a lost anywhere of more than a volt is reason for diving in and checking things out.
Good luck.
Paul
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Cargo Master
Joined: Nov 2009
Posts: 2,364
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From: starship enterprise
Mine is sluggish at idle, need revved up, if fan and ac and lights on, volts drop if idled long time, as soon as revved up, alt. fields and charges. Pretty normal on earlier systems. The farm machinery is the same. at idle it just sucks the battery down if ac and lights on, then once sped up it fields and takes right off.
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Elder User
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Well, I went thru all my electrical connections (grounds also), checked them, cleaned them, reconnected them. Voltage at the battery posts is as it was before, 14.2v but the reading on my dash voltmeter went from just under 13v to just over 13.5v so approx. a .7v improvement. Now I have roughly a .5v differential between battery and gauge as opposed to a 1.3v differential. I think I can live with that.
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